CHRISTOPHER LONG visits the Aga Khan's religious and cultural centre for his 8,000 Ismaili followers in Britain.

If anything seems calculated to cause consternation among London's population it's the sudden appearance of a new building on the skyline. The reaction is hardly surprising. For 30 years we have had one monstrosity after another foisted upon us and almost always they have added insult to the injury of losing once-familiar, often affectionately-regarded streets, houses and public buildings.

Which is why the new Ismaili Centre in South Kensington can be greeted with relief, admiration and much pleasure.

The island of land between Thurloe Place and Cromwell Road, opposite the Victoria & Albert Museum, was a hideous eyesore for as long as many of us can remember. For years it was a derelict site, fit only for use as a car-hire depot behind tatty hoardings and a pre-fab office. And for years the authorities agonised over what would be an acceptable scheme for what was arguably the most prominent and prestigious plot of development land in West London.

It is almost ludicrous to remember that once, in the 1980s, it was thought that this 1,730 sq. m. site would make a suitable home for the National Theatre. One look at the building eventually put up on the South Bank  the acres of space it covers, the massive height and bulk of it and the parking space it needed to provide  shows how inadequate either the site or the theatre would have been if the plan had been executed in South Kensington. Yet it was some measure of the importance of the site, prominently visible on London's main east-west thoroughfare and set in the heart of museum-land, that Bernard Shaw even got as far as laying the foundation stone there.

After that plan was dropped, there were the inevitable applications to build towering blocks of offices and shops that would have dwarfed the quiet, elegant Victorian charm of Thurloe Square and South Kensington as a whole.

Perhaps all along there had been some divine architectural destiny for the Thurloe Place site. When the Aga Khan first saw it as a potential location for a religious and cultural centre for his 8,000 Ismaili followers in Britain, it did not escape his attention that the triangular plot conveniently faces south-east not so much towards Knightsbridge as towards Mecca. But at the same time he was acutely aware that establishing the very first Ismaili centre in the Western world on such an important site as this was fraught with potential hazards.

How would Londoners react to a small, little-known and little-understood religious community taking over such a prestigious position at the centre of the institutional and cultural heart of Britain? Furthermore, what sort of building could possibly answer the needs of both the Ismailis and the English?

Fortunately, by the time the local authorities had granted planning permission, and Lord Soames had laid the foundation stone in the presence of the Aga Khan in 1979, two important things happened in favour of the Ismailis.

First, a remarkable architect had been found. Neville Conder and his team at the Casson Conder Partnership not only won the architectural competition with a design that deeply impressed the Ismailis, but also had a unique knowledge of the site and its environment. By chance their offices were in Thurloe Place, not 50 yards from the site. In addition Conder was also a resident of Thurloe Square.

The second fortuitous event was the sudden interest in Islamic art and culture that developed in Britain as a result of the World of Islam Festival in 1976. Until then it's probably fair to say that very few people in Britain had any clear idea about Islam and the intricate historical and cultural threads that link Shia Muslims with Sunni Muslims and how they in turn have spread, adapted and fragmented their culture throughout Africa, Asia and the Middle East with only the one word 'Allah' to represent those threads today.

Still less did the British know how much British/Christian culture owes to Islam and how, ever since the Middle Ages, much of what we proudly regard as 'English' in fact has direct or indirect roots in the phenomenal and vastly underrated Islamic cultural empire.

Put at its simplest, what the Aga Khan and his community wanted was a modern meeting of East and West. The Ismaili Centre was to be a modern building inspired by traditional Islamic concepts but not a reproduction of Islamic shapes and styles. It was to be a building that contained a cultural meeting place in a succession of public rooms, combined with a Prayer Hall and Council Chambers, which would speak for and identify a small and highly sophisticated group of British Muslims while acknowledging ancient and Eastern origins.

And that's precisely what they got.

In the polished granite surfaces and the jewel-like facets of hundreds of teak-framed panes of bevelled glass, the exterior of the oh-so-un-English Ismaili Centre picks up and perfectly reflects the images of surrounding buildings such as the oh-so-English V&A.

The vertical flame-striped lines etched deep into almost white granite take the eye up to a chamfered sloping roof that throws light (occasionally blue skies) through the stucco-fronted windows of Victorian terraced houses. Yet the sabre-sharp angles of the facade and broken roof-line produce a stark contrast of light and shade that makes the centre look as if it's standing in searing Asian sunlight rather than under a tepid English sky!

Nowhere is there a cross such as we take for granted in usual Christian and Western architecture. Nor are there any of the Greek or Roman references that we are accustomed to see. But everywhere there are surprises: windows, arches, angles and recesses that combine with an almost bizarre juxtaposition of materials to tease and delight the eye. What holds that up? Why is there a window there? What on earth goes on inside?

The last question is a good one. Nothing on the outside tells you what on earth to expect inside  no minarets, no bells to summon the faithful. The only dome in the vicinity is on top of the V&A.

What it does contain is a succession of halls, staircases and landings that draw the visitor further and further towards the heart of the building.

Everything, from the outer entrance hall with its seven-sided fountain, seven-sided pillars and cool, geometrically decorated stone floor, impels the visitor onwards and upwards to a vast Prayer Hall capable of accommodating 1,250 worshippers. To the initiated there are innumerable tiny indicators (such as a minutely changing pattern in the carpet) which progressively prepare the visitor for his approach to this immense inner sanctum.

Between the outer entrance hall and this second-floor Prayer Hall even the uninformed visitor senses an atmosphere of anticipation without knowing quite why. The bright atmosphere becomes more muted as brilliant shafts of seven-sided light descend from unexpected light-wells throwing the simple white plaster walls into dramatic contrast. A repetitive blue-line motif carries one on and up, past a huge Social Hall towards a Shoe Hall where a three-dimensional blue and white honeycomb drops a little lower. Here worshippers exchange their shoes for a coloured cloakroom token before moving on towards the stairs which lead up to the Prayer Hall.

For the first time truly Islamic taste reveals itself in the ornate, carved and mirrored doors that lead into what must be one of the most awe-inspiring rooms to be found in any building in London.

A vast expanse of carpeted floor stretches away to tiled walls, pierced screens and stylised calligraphy. Hundreds of tiny lamps low overhead create an extraordinary and unworldly atmosphere that suspends all sensation of time and place. Ahead, due east, there is no altar, nothing to distract the eye except the constantly repeated word 'Allah', nothing to disrupt the cool, calm and contemplative aura of peace. It's hard to imagine that just three feet beyond the sound-proofed walls of this enormous space there is the busiest thoroughfare of a capital city thousands of miles from the heart of Islam.

Designed by Karl Schlamminger, a German Muslim, this extraordinary room is only flawed by a wall clock that plays a vital part in the religious observance but which might be better suited to the waiting room at Victoria Coach Station.

All in all the Ismaili Centre is a remarkable building that presented Conder and his partners with a site and a challenge that probably come only once in a life-time. For Londoners too the building represents a challenge.

The first question most people have asked is "How much must it all have cost?"

The Ismailis themselves are very reticent on the subject.

The building contract cost in January 1980 was approximately £6.5 million and may have risen by now to as much as £9 million after inflation and final accounts are rendered. But that still doesn't include architectural fees and the furniture and furnishings. The greatest unknown factor is how much the Ismailis paid the GLC for the freehold site in the first place.

What is certain is that the Aga Khan played a considerable part at every stage in the development of his prestigious project and was clearly prepared to invest many millions in this focal point for British Ismailis who used to congregate in cramped quarters in Palace Gate.

The Aga Khan opens and dedicates the building this month. We can be grateful that East and West have met so felicitously in South Kensington.

Captions to original illustrations:

A lift takes visitors up to the third floor roof garden, where a surrounding screen of pale grey granite reflects light into the council chambers, reading room and colonnade. The domed and geometrically decorated ceilings incorporate light wells, and glazed doors open onto the garden and its fountains.

There are no minarets of Islamic domes above the council chambers which overlook the garden. The reading room and council room at the west end of the garden are linked to a glazed colonnade which overlooks an array of flower beds, fountains and water-courses.

The Outer Entrance Hall with its geometrical design and numerical symbolism is dominated by Karl Schammingers seven-sided blue granite fountain.